OVSF codes are designed so that in an ideal environment time synchronised signals that have been spread with OVSF codes do not interfere with each other. However, in practical (non-ideal) environments the orthogonality of these codes is never perfect because:                1. In frequency selective wideband channels the channel delay spread causes multiple delayed replicas of the same transmitted signal to arrive at the receiver. This is owing to obstacles in the environment giving rise to signal reflection and diffraction causing multipath propagation delay, which destroys orthogonality.        2. Even if the cell environment would not cause multipaths, in systems employing multiple transmit antennas these antennas typically introduce several multipath components with fractional chip delay offsets.        
Therefore also systems that employ OVSF codes suffer from intercode interference. In some systems, such as Multiple-Input Multiple-Output (MIMO) systems (see, for example, Huang H., Sandell M., Viswanathan H., “Achieving high data rates on the UMTS downlink shared channel using multiple antennas,” 3G Mobile Communication Technologies Conference, London, March 2001, IEE Conference Publication No. 477, pp. 373-379). This interference can seriously harm the performance of the receiver.